The present invention relates to a method for manufacturing a mask for a color CRT (cathode ray tube), which comprises a plurality of mask members spaced apart from each other at predetermined intervals near a screen, and having a number of apertures through which electron beams can pass.
A mask focusing type CRT is known well as a color CRT of the type described above. In the mask focusing type color CRT, a plurality of mask members which oppose each other at the predetermined intervals are kept at predetermined potentials so as to form electrostatic lenses for electron beams passing through a number of apertures of the mask members. Thus, the electron beams are efficiently used. The mask focusing type CRTs of this type are described in Japanese Utility Model Publication No. 45-4819, Japanese Utility Model Publication No. 47-20451, U.S. Pat. No. 2,971,117, and U.S. Pat. No. 3,398,309.
Another example of a color CRT of the type mentioned above is described in Japanese Patent Publication No. 55-2698. The color CRT comprises double masks wherein which are disposed to prevent mislanding due to thermal deformation caused by a temperature rise of the mask.
In the mask focusing type color CRT or the color CRT which has two mask members, apertures of one mask member must be disposed to correspond to apertures of the other mask member over the entire area thereof. However, manufacture of such a mask is very difficult.
Japanese Patent Publication No. 47-28188 and Japanese Patent Publication No. 47-28189 propose methods for manufacturing a mask having the above structure. However, since a glass insulator is disposed between mask members excluding apertures, forming of the mask is rather poor. Further, the glass insulator is electrically charged by beam bombardment, which adversely affects the electron beams passing through the apertures. Therefore, these methods are not industrially applicable in practice.